Used this yesterday on a flight from Heathrow to JFK on my iPad Air II, works very well. Some details:
Not all titles are available for download, but they are clearly marked and you can navigate to a "downloadable" subcategory to find them all.
The downloads take place in a 'standard' quality that is not HD but looks like HD on a mobile device, same as in iTunes. The 100 minute movie I downloaded was 250MB in size. That's concurrent with iTunes SD download sizes.
The battery usage is very efficient, I watched the movie from end to end and it only used 3% of my battery which dropped from 100% to 97% when it was done. This metric too is similar to iTunes movie viewer native to the iPad.
The on-screen controls are intuitive, what you'd expect.
The downloads have to be viewed within a certain period, I believe it's 5 days or so, so they are more like iTunes rentals than purchases.
All in all I was very happy, it's nice to be able to take a trip and download an entire show season at no cost, similar experience of a season of, say, Mad Men, would cost $20 on iTunes. It's great for the binge viewer.
BJ